Studies on mating structure and kin selection in a subsocial spider mite by the use of molecular and quantitative genetic methods.

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First we conducted a field survey for Schizotetranychus miscanthi Saito in the districts along the Japan Sea, Honsyu Island. For the specimens collected from 18 populations, male aggressiveness was experimentally evaluated. Minimum daily temperature at each district was obtained from AMEDAS data, then the relationship between male aggressiveness and temperature was analyzed. Significant and positive correlation between male aggressiveness and the minimum temperature during winter was obtained. From the analysis on the effect of snow cover, it was re-proved that the winter temperature which may directly affect overwintering probability of the spider mite males (which may reflect the relatedness of males) is an important factor to explain the clinal variation in male aggressiveness of S.miscanthi.Inbreeding experiment for 6 lineages selected from the Shimane population revealed that there is inbreeding depression on female reproductivity. However, there is no such depression in the survival rate of immatures. Because the depression is thought to be a result of heterosis at the grand parent stage, the mating structure of the population tested is thought to be under somewhat inbreeding conditioins.Extraction of DNA was greatly advanced by the use of chitinase. By the use of this new method, much variation in the length of DNA fragment was detected by using PCR method. This finding may enhance the estimation of the relatedness among interacting males in the fields.